Tiltable swivel chair

ABSTRACT

A tiltable swivel chair in which a seat is mounted on a pivot head for tiltable movement about a tilt axis which is normal to a vertical swivel axis. A housing which carries the pivot head also carries a series of compression washers engaging pins projecting from the pivot head to swing the latter forwardly around the tilting axis to a predetermined forward end position. The compression washers are distributed along a horizontal spring axis and the pins projecting from the pivot head compress the washers when the pivot head is swung rearwardly when the seat of the chair is tilted back. The tiltable swivel chair may also include compression washers distributed along a vertical spring axis and engaging stationary pins which project from the housing.

United States Patent [191 Kastholm et al.

[ June 4, 1974 TILTABLE SWIVEL CHAIR 221 Filed: Oct.28, 1971 2: Appl. No; 193,349

FOREIGN PATENTS OR APPLICATIONS 1.072.307 6/1967 Great Britain 248/378 Primary Examiner-William H. Schultz Attorney, Agent, or FirmB1um Moscovitz Friedman & Kaplan [5 7 ABSTRACT A tiltable swivel chair in which a seat is mounted on a pivot head for tiltable movement about a tilt axis which is normal to a vertical swivel axis. A housing which carries the pivot head also carries a series of compression washers engaging pins projecting from the pivot head to swing the latter forwardly around the tilting axis to a predetermined forward end position. The compression washers are distributed along a horizontal spring axis and the pins projecting from the pivot head compress the washers when the pivot head is swung rearwardly when the seat of the chair is tilted back. The tiltable swivel chair may also include compression washers distributed along a vertical spring axis and engaging stationary pins which project from the housing.

11 Claims, 7 Drawing Figures 'PATENTEUJUH 419M 3.814.369

sum 1' or 2 INVENTORS l/ZRGE/V Maw/04M ATTORNEY 1 TILTABLE SWIVEL CHAIR BACKGROUND OF THE INVENTION The present invention relates to tiltable swivel chairs.

In particular, the present invention relates to a tilting mechanism to be used in such chairs.

As is well known tiltable swivel chairs have a mechanism enabling the seats of the chairs to be swivelled about a vertical axis while at the same time enabling the seat to be tilted rearwardly and forwardly. Generally such mechanisms will include spring structures for tilting the seat forwardly to a predetermined forward end position. When the seat is tilted rearwardly from the forward end position the spring opposes this rearward tilting movement so that the seat will always be urged to tilt forwardly to its forward end position.

One of the drawbacks encountered with conventional mechanisms of this type is that they include relatively heavy coil springs which are exposed and which are difficult to assemble with the remainder of the mechanism which is relatively complex. Adjustment of the spring force is difficult to carry out and the transmission between the spring and the chair seat is composed of a number of elements rendering the structure expensive to manufacture and assemble.

SUMMARY OF THE INVENTION It is accordingly a primary object of the present invention to provide for a tiltable swivel chair a tilt mechanism which will avoid the above drawbacks.

In particular, it is an object of the invention to provide a tilt mechanism of this type which is exceedingly simple and inexpensive.

Also it is an object of the present invention to provide a tilt mechanism which can have the spring force thereof easily adjusted in a highly precise manner.

Furthermore it is an object of the invention to provide a tilt mechanism of the above type which is protected in a housing.

Furthermore it is an object of the present invention to provide a tilt mechanism which has a wide range of adjustment while at the same time being exceedingly compact so that only a relatively small space beneath the seat is required for the mechanism of the invention.

According to the invention a pivot means is adapted to be fastened to the underside of a seat. A housing means supports the pivot means for tilting movement about a predetermined tilt axis fowardly toward and rearwardly away from a predetermined forward end position. A support means supports the housing means for rotary movement about a swivel axis which is normal to the tilt axis. A springy compression washer means is situated within the housing means, and a mounting means is carried by the housing means for mounting the compression washer means for compression and expansion along a spring axis which is perpendicular to the tilt axis. A transmission means which is carried by the pivot means engages the compression washer means for compressing the latter to an increasing extent as the pivot means is tilted rearwardly away from the forward end position with the compression washer means acting through the transmission means and the pivot means to urge the latter forwardly about the tilt axis toward the forward end position.

BRIEF DESCRIPTION OF DRAWINGS The invention is illustrated by way of example in the accompanying drawings which form part of this application and in which:

FIG. 1 is a perspective illustration of a tiltable swivel chair provided with the structure of the invention;

FIG. 2 is a fragmentary sectional elevation taken along line 2-2 of FIG. 1 in the direction of the arrows and showing at an enlarged scale, as compared to FIG. 1, the mechanism of the present invention;

FIG. 3 shows the structure of FIG. 2 when it is tilted rearwardly from the forward end position;

FIG. 4 is a fragmentary sectional plan view taken along line 4-4 of FIG. 2 in the direction of the arrows and showing details of the structure;

FIG. 5 is a sectional elevation of another embodiment of the invention;

FIG. 6 is a sectional plan view taken along line 66 of FIG. 5 in the direction of the arrows; and

FIG. 7 shows the structure of FIG. 5 as seen from the right of FIG. 5.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to the drawings, there is illustrated in FIG. 1 a tiltable swivel chair 10 having a seat 12 to the underside of which is fixed the mechanism 14 of the invention. This mechanism 14 is carried by a sleeve 16 which in turn is carried by the feet 18 fixed to and radiating from the lower end region of the vertical sleeve 16.

Referring to FIG. 2, the mechanism 14 includes a pivot means 20 in the form of a block 22 which forms a pivot head. This pivot head 22 of the pivot means 20 fixedly carries a mounting plate 24 which is adapted to be fastened in a known way to the underside of the seat 12 so that the latter is compelled to tilt with the pivot head 22.

A housing means 26 of the mechanism 14 supports the pivot means 20 for tilting movement forwardly toward and rearwardly away from the forward end position shown in FIG. 2 about a horizontal tilt axis which is normal to the plane of FIG. 2. This tilt axis coincides with the axis of an elongated pivot pin 28 which extends between and is carried by a pair of upstanding opposed wall portions 30 of the housing means 26. This housing means 26 includes a lower block 32 fixed to the interior of the tubular outer wall of the housing means 26. The block 32 is fixed to the top end of a vertical shaft 34 which is supported for rotary movement about its axis in the sleeve 16. This axis of the shaft 34 forms a swivel axis coaxially surrounded by the tubular housing 26 and around which the entire housing 26 can swivel. The swivel axis of the shaft 34 thus coincides with the central axis of the housing 26 and is normal to the tilt axis which coincides with the axis of the pivot rod 28. This latter rod extends through a suitable bore extending transversely through the block which forms the pivot head 22.

Forwardly of the upstanding wall portions 30 of the upper region of the housing 26, this housing has an upwardly directed limiting surface 36 directed toward the downwardly directed bottom surface 38 of the pivot head 22. Thus, when the surface 38 engages the surface 36 the pivot head 22 cannot tilt further in a foward direction so that in this way the forward end position of the pivot means 20 is determined. Thus the pivot means can tilt about the rod 28 rearwardly from and forwardly toward the forward end position shown in FIG. 2. The pivot head 22 is shown tilted rearwardly from its forward end position in FIG. 3.

The springy compression washer means 40 is situated in the interior of the housing means 26. This housing means 26 has not only the tubular configuration surrounding the swivel axis but also a tubular extension 42 fixed to the main tubular portion of the housing 26 and extending horizontally therefrom. The wall of the housing 26 is formed with an opening registering with the left open end of the tubular housing extension 42, as viewed in FIG. 2. The compression washer means 40 is accommodated not only in the interior of the vertically extending tubular part of the housing 26 but also in the interior of the horizontally extending tubular extension 42 thereof.

A mounting means 44 is carried by the housing means 26 for mounting the compression washer means 40 for compression and expansion along a horizontal spring axis which is normal to the vertical swivel axis while at the same time being perpendicular to and situated beneath the horizontal tilt axis. This mounting means 44 includes an elongated rod 46 extending through the series of compression washers 48 which form the compression washer means 40. These washers 48 are slightly dished springy washers known as Bell velle springs. The compression washers 48 are arranged back-to-back in groups of two, as is apparent from FIGS. 24. Thus, the rod 46 of the mounting means 44 extends through the series of compression washers 48 to support the latter for compression and expansion along the horizontal axis of the rod 46 which forms the horizontal'spring axis. t

A nut 50 is fixed to the outer end of the tubular extension 42 in the interior thereof. The internal threads of the nut 50 are in threaded engagement with the external threads on an enlarged right end portion 52 of the rod '46, this'enlarged end portion engaging the right end washer of the series shown in FIG. 2. The right end face of the enlarged end 52 of the rod 46 is accessible at the front of the chair, as is apparent from FIG. I. This right end face is formed with a transverse diametral groove for receiving the tip of the screw driver so that the rod 46 can be longitudinally adjusted for adjusting the spring force.

A transmission means 54 is provided for transmitting force of the compression washer means 40 to the pivot head 22. This transmission means is carried by the pivot head 22 and engages the left end compression washer of the series shown in FIG. 2. The transmission means 52 includes a pair of vertically extending pins 56 fixed to and extending downwardly from the pivot head 22. These pins 56 are situated in the interior of the housing 26 and extend to opposite sides of the rod 46.

Thus the rod 46 is received between the pins 56 while the latter engage the left end compression washer 48, as viewed in FIGS. 2-4.

Thus, with this construction when the seat 12 is tilted rearwardly away from its forward end position the pivot head 22 will tilt in a counterclockwise direction away from the position of FIG. 2, and as the extent of'rearward tilting increases the compression of the compression washer means 40 increases as a result of the engagement of the compression washer means 40 by the transmission means 54 extending from the pivot means 20. The compressed condition of the compression washer means 40 is particularly apparent from FIG. 3. It will be noted that during compression the series of washers 48 assume a substantially flat condition progressing from the right toward the left, as viewed in FIG. 3, as the extent of compression increases. Thus, the compression washer means 40 continuously acts through the transmission means 54 to urge the pivot means 20 back toward its forward end position shown in FIG. 2.

At the left endthe rod 46 is shown in the drawings engaging an inner surface of the housing 26, so that the parts are shown in the condition where the compression washer means 40 provides its maximum spring force. In order to reduce the spring force the adjusting means formed by the nut 50 and the threaded enlarged portion 52 of rod 46 can bemanipulated so as to advance the rod 46 toward the right, as viewed in FIG. 2, and in this way the spring force may be reduced. It is thus apparent that with the structure of the invention an exceedingly simple and compact mechanism 14 is provided. The compression washer means 40 is protected in the interior of the housing means 26. It is an exceedingly simple matter to adjust the force of the spring since the outer end surface of the enlarged part 52 of rod 46 is freely accessible at the front of the chair just beneath the seat 12 thereof. By using the series of compression washers 48 all of the problems involved in the use of heavy coil springs are eliminated. Before the pivot head 22 is assembled with the housing 26 bythe rod 28 it is a simple. matter to quickly mount the series of compression washers 48 on the rod 46 while the left end thereof, as viewed in FIG. 2, is spaced to the right of the left wall portion of the housing 26, as viewed in FIG. 2. Then the pivot head 22 can be assembled with the housing 26 and the transmission pins 56 can be situated to the left of the series of compression washers 48. Thus an exceedingly simple and effective assembly can be carried out with this construction. Moreover, it is also a simple matter, upon removal of the pivot head 22, to add compression washers to the series or to remove compression washers therefrom in order to achieve an exceedingly satisfactory adjustment of the spring force. Through the addition or removal of the spring washers a relatively coarse adjustment in the spring force can be achieved while the turning of the rod 46 with respect to the nut 50 will achieve a fine adjustment. It is furthermore to be noted that the compression of the spring washers 48 between the transmission pins 56 and the enlarged threaded portion 52 of the rod 46 enables these spring washers to function so as to maintain the rod 46 in its adjusted position with respect to the nut 50.

It is furthermore to be noted that in the fully expanded position of the compression washer means 40 the transmission pins 56 directly engage the inner surface of the housing 26 at a region thereof distant from the enlarged end portion 52 of the rod 46. Thus, by displacing the rod 46 to the right, as viewed in FIG. 2, the shoulder formed at the left end of the enlarged portion 52 of the rod 46 will be displaced to the right, thus increasing the distance between the transmission pins 56 and this shoulder so as to increase the longitudinal space in which the spring washers 48 are accommodated-and thus reduce the spring force.

Referring now to FIGS. 5-7, the embodiment of the invention which is illustrated therein includes a housing means 126 which corresponds to the housing means 26 and is supported in precisely the same way on the base unit l6, 18. This housing means 126 carries at its upper end a pivot means 120 for the seat 124. The pivot means 120 of this embodiment includes an elongated pivot pin 128 fixed at its opposed ends to the upstanding ears 130 of the housing means 126. The pivot 128 extends across the space between the upstanding ears and through a bore which is formed in a block 122 of the pivot means 120, this block being fixed to and extending downwardly from the seat 124 and being received in the upper hollow portion of the housing means 126.

At its forward end region the block 122 is formed with an elongated notch 90 which communicates with the bottom end of the block 122 and thus with the hollow interior of the housing means 126. This notch serves to receive the eye end of an elongated rod 146. The block 122 carries a pin 92 which extends across the notch 90 through the eye of the rod 146. At its bottom end the rod 146 is threaded and carries a nut 152.

At its upper end region, just beneath the block 122 the rod 146 passes freely between a pair of horizontally extending pins 156 which are fixed to the housing means 126 and extend horizontally therefrom to the left, as viewed in FIG. 5, defining between themselves a space through which the rod 146 freely extends, as is clearly apparent from FIG. 7. The manner in which the rod 146 extends between the pins 156 is also clearly apparent from 6.

Between the nut 152 and the pins 156 the rod 146 passes through aspringy compression washer means 140 formed in this embodiment also by a series of compression washers 148 known as Bellvelle springs. These washers 148 are also arranged back-to-back in groups of two.

It is thus possible to achieve with this embodiment also the advantages which are achieved with the embodiment described above and shown in detail in FIGS. 2-4. The seat 124 can be tilted about the tilt axis defined by the axis of the pivot pin 128 for example between the solid and dotted line positions indicated in FIG. 5. When the seat is tilted the rod 146 is pulled upwardly, compressing the compression washer means 140 between the nut 152 and the pins 156 to an increasing extent as the seat is tilted further in a counterclockwise direction about the pin 128, as viewed in FIG. 5. Of course the springs 148 will always seek to return the seat 124 to the solid line position where it is horizontal and where its front edge rests on and engages the top edge of the housing means 126 so that in this way these edges form a limiting means for limiting the swinging of the seat 124 back to its normal position.

, It will be noted that with this embodiment also the compression washer means 140. is completely housed and protected from the outside. Furthermore it is a simple matter to adjust the compression by turning the nut 152. For this purpose the housing 126 may be formed with an opening 127 through which access may be had directly to the nut 152 or the pin 128 can be removed and the entire seat with the structure carried thereby can be displaced readily out of the housing 126 so that the operator can then turn the nut 152 and replace the components in a rapid convenient manner.

We claim:

1. In a tiltable swivel chair, pivot means adapted to be fixed to a seat of the chair at the underside of said seat, housing means supporting said pivot means for tilting movement about a predetermined horizontal tilt axis rearwardly from and forwardly toward a given forward end position, support means supporting said housing means for rotary movement about a vertical swivel axis perpendicular to said tilt axis, springy compression washer means situated in said housing means, mounting means for mounting said compression washer means for compression and expansion along a horizontal spring axis perpendicular to said tilt axis, and transmission means engaging said compression washer means for transmitting tilting of said pivot means about said tilt axis to said compression washer means for compressing the latter horizontally to an increasing extent as said pivot means is tilted rearwardly away from said forward end position, said compression washer means acting through said transmission means on said pivot means for urging the latter forwardly toward said forward end position, said compression washer means including a series of compression washers arranged backto-back in groups of two, said mounting means includ ing an elongated rod extending through the series of compression washers, and adjusting means coacting with said rod for adjusting the longitudinal position thereof in said housing means to adjust said compression washer means, said adjusting means including an end portion of said rod which is of a diameter larger than the remainder of the rod and has an inner end surface engaging an end washer, said end portion being externally threaded and having an outer end surface accessible at the exterior of said housing means and a nut carried by said housing and surrounding and engaging the threads of said end portion of said rod so that turning of the latter with respect to said nut will adjust the longitudinal position of said rod.

2. The combination of claim 1 and wherein said transmission means includes a pair of pins carried by said pivot means for swinging movement therewith about said tilt axis and extending to opposite sides of said rod. respectively, the latter extending between said pins and said pins engaging an end washer of the series of compression washers distant from said nut, said housing having a stationary surface engaging said pivot means to determine an end position of the seat.

3. The combination of claim 2 and wherein said tilt axis is situated above said spring axis;

4. In a tiltable swivel chair, pivot means adapted to be fixed to a seat of the chair at the underside of said seat, housing means supporting said pivot means for tilting movement about a predetermined horizontal tilt axis rearwardly from and forwardly toward a given forward end position, support means supporting said housing means for rotary movement about a vertical swivel axis perpendicular to said tilt axis, springy compression washer means situated in said housing means, mounting means for mounting said compression washer means for compression and expansion along a horizontal spring axis perpendicular to said tilt axis, and transmission means engaging said compression washer means for transmitting tilting of said pivot means about said tilt axis to said compression washer means for compressing the latter horizontally to an increasing extent as said pivot means is tilted rearwardly away from said forward end position, said compression washer means acting through said transmission means on said pivot means for urging the latter forwardly toward said forward end position, said compression washer means ineluding a series of compression washers arranged backto-back in groups of two, said mounting means including'an elongated rod extending through the series of compression washers, and adjusting means coacting with said rod for adjusting the longitudinal position thereof in said housing means to adjust said compression washer means, said adjusting means including an end portion of said rod which is externally threaded and which has end face accessible at the exterior of said housing means and a nut carried by said housing and surrounding and engaging the threads of said end portion of said rod so that turning of the latter with respect to said nut will adjust the longitudinal position of said rod, said transmission means including a pair of pins carried by said pivot means for swinging movement therewith about said tilt axis and extending to opposite sides of said rodfrespectively, the latter extending between said pins and said pins engaging an end washer of the series of compression washers, said housing having a stationary surface engaging said pivot means to determine an end position of the seat, said housing means being of a tubular configuration coaxially surrounding said swivel axis and including a tubular extension surrounding said spring axis and accommodating at least some of the compression washers in its interior.

5. The combination of claim 4 and wherein said tubular extension fixedly carries said nut at the region of a free end of said tubular extension.

' 6. In a tiltable swivel chair, pivot means adapted to be fixed to a seat of the chair at the underside of said seat, housing means supporting said pivot means for tilting movement about a predetermined tilt axis rearwardly from and forwardly toward a given forward end position, support means supporting said housing means forrotary movement about a swivel axis perpendicular to said tilt axis, springy-compression washer means situated in said housing means, mounting means for mounting said compression washer means for compression and expansion along a spring axis perpendicular to said tilt axis, and transmission means engaging said compression washer means for transmitting tilting of said pivot means-about said tilt axis to said compression washer means for compressing the latter to an increasing extent as said pivot means is tilted rearwardly away from said forward end position, said compression washer means acting through said transmission means on said pivot means for urging the latter forwardly toward said forward end position, said housing means including at an upper region a pair of opposed upstanding wall portions extending across said tilt axis and between which said pivot means is located, said pivot means including a pivot head having a bottom surface directed toward said compression washer means, and said housing means having an upper end surface situated beneath said bottom surface of said pivot head for engaging the latter to determine said forward end position.

7. The combination of claim 6 and wherein said swivel axis and spring axis are substantially parallel to each other. I 8. The combination of claim 7 and wherein said mounting means includes an elongated rod extending downwardly from said pivot means along the interior of said housing means. v

9. The combination of claim 8 and wherein said compression washer means includes a series of compression washers arranged back-to-back in groups of two, said rod extending through said series of compression washers, and said transmission means including a pair of pins fixedly carried by said housing in the interior thereof over said washers,- said pins extending across said rod and the latter extending freely through a space defined between said pins, the upper end of the series of compression washers engaging said pins.

10. The combination of claim 9 and wherein said rod threadedly carries at its bottom end portion a nut engaging the lower end of the series of compression washers andforming an adjusting means for adjusting saidwashers.

11. The combination of claim 10 and wherein said pivot means is pivotally connected with said rod at an upper end thereof so that when said pivot means swings about said tilt axis said rod is pulled upwardly with respect to said pins of said transmission means for compressing the washers between said pins and said nut. 

1. In a tiltable swivel chair, pivot means adapted to be fixed to a seat of the chair at the underside of said seat, housing means supporting said pivot means for tilting movement about a predetermined horizontal tilt axis rearwardly from and forwardly toward a given forward end position, support means supporting said housing means for rotary movement about a vertical swivel axis perpendicular to said tilt axis, springy compression washer means situated in said housing means, mounting means for mounting said compression washer means for compression and expansion along a horizontal spring axis perpendicular to said tilt axis, and transmission means engaging said compression washer means for transmitting tilting of said pivot means about said tilt axis to said compression washer means for compressing the latter horizontally to an increasing extent as said pivot means is tilted rearwardly away from said forward end position, said compression washer means acting through said transmission means on said pivot means for urging the latter forwardly toward said forward end position, said compression washer means including a series of compression washers arranged back-to-back in groups of two, said mounting means including an elongated rod extending through the series of compression washers, and adjusting means coacting with said rod for adjusting the longitudinal position thereof in said housing means to adjust said compression washer means, said adjusting means including an end portion of said rod which is of a diameter larger than the remainder of the rod and has an inner end surface engaging an end washer, said end portion being externally threaded and having an outer end surface accessible at the exterior of said housing means and a nut carried by said housing and surrounding and engaging the threads of said end portion of said rod so that turning of the latter with respect to said nut will adjust the longitudinal position of said rod.
 2. The combination of claim 1 and wherein said traNsmission means includes a pair of pins carried by said pivot means for swinging movement therewith about said tilt axis and extending to opposite sides of said rod, respectively, the latter extending between said pins and said pins engaging an end washer of the series of compression washers distant from said nut, said housing having a stationary surface engaging said pivot means to determine an end position of the seat.
 3. The combination of claim 2 and wherein said tilt axis is situated above said spring axis.
 4. In a tiltable swivel chair, pivot means adapted to be fixed to a seat of the chair at the underside of said seat, housing means supporting said pivot means for tilting movement about a predetermined horizontal tilt axis rearwardly from and forwardly toward a given forward end position, support means supporting said housing means for rotary movement about a vertical swivel axis perpendicular to said tilt axis, springy compression washer means situated in said housing means, mounting means for mounting said compression washer means for compression and expansion along a horizontal spring axis perpendicular to said tilt axis, and transmission means engaging said compression washer means for transmitting tilting of said pivot means about said tilt axis to said compression washer means for compressing the latter horizontally to an increasing extent as said pivot means is tilted rearwardly away from said forward end position, said compression washer means acting through said transmission means on said pivot means for urging the latter forwardly toward said forward end position, said compression washer means including a series of compression washers arranged back-to-back in groups of two, said mounting means including an elongated rod extending through the series of compression washers, and adjusting means coacting with said rod for adjusting the longitudinal position thereof in said housing means to adjust said compression washer means, said adjusting means including an end portion of said rod which is externally threaded and which has end face accessible at the exterior of said housing means and a nut carried by said housing and surrounding and engaging the threads of said end portion of said rod so that turning of the latter with respect to said nut will adjust the longitudinal position of said rod, said transmission means including a pair of pins carried by said pivot means for swinging movement therewith about said tilt axis and extending to opposite sides of said rod, respectively, the latter extending between said pins and said pins engaging an end washer of the series of compression washers, said housing having a stationary surface engaging said pivot means to determine an end position of the seat, said housing means being of a tubular configuration coaxially surrounding said swivel axis and including a tubular extension surrounding said spring axis and accommodating at least some of the compression washers in its interior.
 5. The combination of claim 4 and wherein said tubular extension fixedly carries said nut at the region of a free end of said tubular extension.
 6. In a tiltable swivel chair, pivot means adapted to be fixed to a seat of the chair at the underside of said seat, housing means supporting said pivot means for tilting movement about a predetermined tilt axis rearwardly from and forwardly toward a given forward end position, support means supporting said housing means for rotary movement about a swivel axis perpendicular to said tilt axis, springy compression washer means situated in said housing means, mounting means for mounting said compression washer means for compression and expansion along a spring axis perpendicular to said tilt axis, and transmission means engaging said compression washer means for transmitting tilting of said pivot means about said tilt axis to said compression washer means for compressing the latter to an increasing extent as said pivot means is tilted rearwardly away from said forward end position, saiD compression washer means acting through said transmission means on said pivot means for urging the latter forwardly toward said forward end position, said housing means including at an upper region a pair of opposed upstanding wall portions extending across said tilt axis and between which said pivot means is located, said pivot means including a pivot head having a bottom surface directed toward said compression washer means, and said housing means having an upper end surface situated beneath said bottom surface of said pivot head for engaging the latter to determine said forward end position.
 7. The combination of claim 6 and wherein said swivel axis and spring axis are substantially parallel to each other.
 8. The combination of claim 7 and wherein said mounting means includes an elongated rod extending downwardly from said pivot means along the interior of said housing means.
 9. The combination of claim 8 and wherein said compression washer means includes a series of compression washers arranged back-to-back in groups of two, said rod extending through said series of compression washers, and said transmission means including a pair of pins fixedly carried by said housing in the interior thereof over said washers, said pins extending across said rod and the latter extending freely through a space defined between said pins, the upper end of the series of compression washers engaging said pins.
 10. The combination of claim 9 and wherein said rod threadedly carries at its bottom end portion a nut engaging the lower end of the series of compression washers and forming an adjusting means for adjusting said washers.
 11. The combination of claim 10 and wherein said pivot means is pivotally connected with said rod at an upper end thereof so that when said pivot means swings about said tilt axis said rod is pulled upwardly with respect to said pins of said transmission means for compressing the washers between said pins and said nut. 